Magnetic Spirals in Accretion Flows Originated from Misaligned Magnetic Fields

Misalignment between rotation and magnetic fields has been suggested to be one type of physical mechanism that can ease the effects of magnetic braking during the collapse of cloud cores leading to the formation of protostellar disks. However, its essential factors are poorly understood. Therefore, we perform a more detailed analysis of the physics involved. We analyze existing simulation data to measure the system torques, mass accretion rates, and Toomre Q parameters. We also examine the presence of shocks in the system. While advective torques are generally the strongest, we find that magnetic and gravitational torques can play substantial roles in how angular momentum is transferred during the disk formation process. Magnetic torques can shape the accretion flows, creating two-armed magnetized inflow spirals aligned with the magnetic field. We find evidence of an accretion shock that is aligned according to the spiral structure of the system. Inclusion of ambipolar diffusion as explored in this work has shown a slight influence in the small-scale structures but not in the main morphology. We discuss potential candidate systems where some of these phenomena could be present.

Color map of advective torque (left panels) overlaid by velocity (arrows) and column density (yellow contours) and magnetic torque (right panels) overplotted by magnetic field (arrows) and column density (yellow contours) on the midplane of various models. 
Column density (in logarithms of g/cm2) of the leaking spiral model at 148.3 (left panel) and 154.3 (central panel) kyr, showing the presessing structure. Density (isosurfaces) with two embedded magnetic field lines (gray curves) whose start points are selected within the inner and outer disks for each (right panel).
Toomre Q at the midplane of the clear spiral model at 149.9 kyr (left panel) and the zoomed-in view (central panel). White represents Q = 1. Density overlaid by fitted spirals; the one-armed spiral in the inner region (blue curve) and the two-armed spiral in a more outer region (red curve) are fitted (right panel).
Face-on view of logaritms of column density (g/cm2) for the clear spiral model with ambipolar diffusion at 135.0 kyr (left panel). The residual column density by subtracting the annular mean from the column density of the same model at 128.0 kyr, and the cutoff inner and outer radii in pure blue are 25 and 125 au, respectively (right panel).

Related Publications

  • Wang WVäisälä MSShang HKrasnopolsky R; Li Z-Y; Lam KH; Yuan F, “Magnetic Spirals in Accretion Flows Originated from Misaligned Magnetic Fields” , ApJ: 928(1), id.85 (23pp), Mar, 2022 [SCI] ( ADS | Fulltext )
  • Väisälä MSShang HKrasnopolsky RLiu S-Y; et al., “Time Evolution of 3D Disk Formation with Misaligned Magnetic Field and Rotation Axes”, ApJ: 873(2), id. 114 (22 pp.), Mar, 2019 [SCI] ( ADSFulltext )
  • Li Z-Y; Krasnopolsky R; Shang H, “Does Magnetic-field-Rotation Misalignment Solve the Magnetic Braking Catastrophe in Protostellar Disk Formation?”, ApJ: 774(1), 82, Sep 1, 2013 [SCI] ( ADS | Fulltext )